JP3642060B2 - Image reading device - Google Patents

Description

(Technical field)
[0001]
The present invention relates to an image reading apparatus.
(Background technology)
[0002]
2. Description of the Related Art Conventionally, there is known an image reading apparatus that reads a document such as paper placed on a transparent document table such as glass and outputs it as image data. In an image reading apparatus, for example, light from a document is converted into an electrical signal by using a line sensor as an imaging unit in which photoelectric conversion elements such as CCDs are linearly arranged in the main scanning direction. Since the electrical signal output from the line sensor is an analog electrical signal, it is converted into a digital electrical signal by the A / D converter. The electrical signal converted into digital is subjected to various corrections such as gamma conversion or shading correction, and then output as digital image data to a personal computer outside the image reading apparatus (hereinafter referred to as “personal computer”). Is done.
[0003]
When a color image is read by the image reading apparatus having the above configuration, analog electrical signals of R, G, and B colors are input from the line sensor to the A / D converter. The input color signals are output from the A / D converter as digital electric signals in accordance with the timing of the clock signal supplied to the A / D converter.
For example, when the output of each color is a 12-bit image reading apparatus, as shown in FIG. 4, the A / D conversion unit 100 is provided with 12 terminals D0 to D11 on the output side. The A / D conversion unit 100 and the image data creation unit 110 are connected by a connection line 120.
As an output gradation corresponding to an analog electrical signal input to the A / D conversion unit 100 for a certain clock signal, for example, a “Hi” digital electrical signal is simultaneously output from the terminals D0 to D7. . As the output gradation of the A / D converter 100 corresponding to the next clock signal, the “Hi” digital signal is output from the terminals D0 to D2, and the “Low” digital signal is output from the terminals D3 to D11. Suppose that it is output.
At this time, the digital electric signal is maintained in the “Hi” state at the terminals D0 to D2. On the other hand, the transition from “Hi” to “Low” is performed from D3 to D7, and the “Low” state is maintained from D8 to D11.
[0004]
By the way, since the digital electrical signal output from the A / D converter 100 has a high frequency, the output digital electrical signal shifts from “Hi” to “Low” or from “Low” to “Hi”. The A / D converter 100 generates electromagnetic radiation noise (hereinafter, electromagnetic radiation noise is referred to as “EMI:”). In particular, for example, digital electrical signals output from adjacent terminals of the A / D converter 100 such as D1 and D2, D2 and D3, etc. are simultaneously synchronized with the clock signal from “Hi” to “Low” or “Low”. ”To“ Hi ”, there is a problem that EMI is amplified and noise increases.
When EMI occurs, there is a possibility that noise is included in the digital image data, and there is a problem that the image quality of the image read by the image reading apparatus is deteriorated.
In addition, in order to prevent the generation of EMI, methods such as mounting an EMI filter or shielding a wiring can be considered. However, when a member such as an EMI filter or a shield is added, the structure becomes complicated, and it is necessary to secure a space for arranging them, which increases the size of the image reading apparatus and increases the cost due to the addition of the member. There is a problem that arises.
Accordingly, an object of the present invention is to provide an image reading apparatus that reduces the EMI with a simple structure and low cost without increasing the size, and improves the image quality of the read image.
(Disclosure of the Invention)
[0005]
According to the image reading apparatus of the first aspect of the present invention, the rising or falling timing of the digital electric signal output from the A / D conversion unit is set between the A / D conversion unit and the image data creation unit. A delay circuit is provided to make it uneven . For this reason, the rising or falling timing of the digital electrical signal output from the A / D converter differs between adjacent terminals. As a result, the EMI is amplified even when the digital electrical signal output from the A / D converter simultaneously shifts from “Hi” to “Low” or “Low” to “Hi” at the adjacent output terminals. The generated EMI can be reduced.
[0006]
Further, since the EMI can be reduced by arranging the delay circuit, it is not necessary to add an EMI filter or a wiring shield, for example.
Therefore, EMI can be reduced with a simple structure and low cost without increasing the size. Further, by reducing EMI, noise included in the image data is reduced, and the image quality of the read image can be improved.
According to the image reading apparatus of the second aspect of the present invention, the delay circuits are arranged on every other connecting line connecting the output terminal and the image data creating unit. For this reason, the rising or falling timing of the digital electric signal is shifted between adjacent terminals, and EMI amplification can be reduced. Further, since the number of delay circuits arranged can be reduced, an increase in cost can be suppressed.
[0007]
According to the image reading apparatus of the third aspect of the present invention, the delay circuit has the resistance element and the capacitor element. Since these resistance elements and capacitor elements are inexpensive, an increase in cost can be suppressed by arranging a delay circuit. In addition, since the resistance element and the capacitor element are small in size, they can be easily mounted on the substrate of the A / D converter or the image reading apparatus itself, and the image reading apparatus can be prevented from increasing in size.
[0008]
According to the image reading apparatus of the fourth aspect of the present invention, the resistance element and the capacitor element arranged in the delay circuit have the same resistance value and the same capacitance value. Therefore, the configuration of the delay circuit is easy. Therefore, an increase in the cost of the image reading apparatus can be suppressed.
[0009]
According to the image reading apparatus of the fourth aspect of the present invention, the delay circuit includes the resistance element and the capacitor element. Since these resistance elements and capacitor elements are inexpensive, an increase in cost can be suppressed by arranging a delay circuit. In addition, since the resistance element and the capacitor element are small in size, they can be easily mounted on the substrate of the A / D converter or the image reading apparatus itself, and the image reading apparatus can be prevented from increasing in size.
[0010]
(Best Mode for Carrying Out the Invention)
[0011]
Hereinafter, a plurality of examples showing embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
An image reading apparatus according to a first embodiment of the present invention is shown in FIG. The image reading apparatus 1 according to the first embodiment is a flat bed type image reading apparatus.
As shown in FIG. 2, the image reading apparatus 1 includes a carriage 20 inside a box-shaped main body 10. A document table 11 is disposed above the main body 10. A document 2 to be read is placed on the side opposite to the carriage 11 of the document table 11. Inside the main body 10 is provided a carriage 20 that can be reciprocated in the sub-scanning direction in parallel with the document table 11 by a driving device 21.
[0012]
The carriage 20 includes a light source 22, a mirror 23, a condenser lens 24, a line sensor 25 as an imaging unit, an A / D conversion unit 40, and a buffer 26. The mirror 23 is provided to reflect the light from the document 2 collected on the line sensor 25 and to increase the optical path length. The condensing lens 24 condenses the light from the document 2 on the line sensor 25. As the line sensor 25, a charge storage type optical sensor in which a plurality of pixels such as a CCD are linearly arranged perpendicular to the moving direction of the carriage 20 is used.
[0013]
The light source 22 is provided perpendicular to the moving direction of the carriage 20, and a fluorescent lamp or the like is used. The light emitted from the light source 22 is reflected by the surface of a reflective original such as paper and is incident on the line sensor 25. The A / D converter 40 converts the analog electrical signal output from the line sensor 25 into a digital electrical signal. The buffer 26 improves the drive capability of the digital electric signal output from the A / D conversion unit 40.
[0014]
A document guide 12 is provided around the document table 11 to position the placement position of the document 2 to be read and to restrict the movement of the document 2 when the document is read. A white reference 13 having a highly reflective uniform reflection surface is provided at the end of the document table 11 in the carriage movement direction.
[0015]
A data processing unit 30 is mounted inside the main body 10. The data processing unit 30 includes a CPU (Central Processing Unit) 31, a RAM (Random Access Memory) 32, a ROM (Read Only Memory) 33, and an image data creation unit 35. The CPU 31 performs overall control of the image reading apparatus 1 such as control of driving of the carriage 20, control of blinking of the light source 22, and processing of image data created by the image data creation unit 35. The RAM 32 temporarily stores image data read by the line sensor 25 and the like. The ROM 33 stores a computer program for controlling each part of the image reading apparatus 1 by the CPU 31.
[0016]
The image data creation unit 35 includes a shading correction unit, a gamma correction unit, and other correction units (not shown). The shading correction unit uses the data obtained by reading the white reference 13 before starting to read the digital signal output from the A / D conversion unit 40, or the sensitivity variation for each pixel of the line sensor 25, or The variation in the amount of light in the main scanning direction of the light source 22 is corrected. The gamma correction unit performs gamma correction using a predetermined gamma function, and converts the digital light amount signal subjected to the shading correction into digital image data. Other correction units perform various conversions such as color correction, edge enhancement, and area enlargement / reduction.
Digital image data created by the image data creation unit 35 is output from an interface 14 provided in the main body 10 to an image processing apparatus such as a personal computer 3 connected to the outside.
[0017]
Next, the A / D conversion unit 40 and the delay circuit 50 disposed between the A / D conversion unit 40 and the image data creation unit 35 will be described.
The A / D converter 40 converts an analog electrical signal into a digital electrical signal. The analog electrical signal output from the line sensor 25 is a voltage value indicating the amount of electric charge accumulated in each pixel constituting the line sensor 25. In order to create digital image data in the image data creation unit 35, it is necessary to convert an analog electrical signal output from the line sensor 25 into a digital electrical signal.
As shown in FIG. 1, an electrical signal corresponding to each color of R (red), G (green), and B (blue) is input from the line sensor 25 to the A / D converter 40. In FIG. 1, the buffer 26 is not shown.
In the A / D converter 40, a digital electric signal having a plurality of gradations is created based on the voltage value of the analog electric signal input from the line sensor 25. In the case of the present embodiment, the gradation of the digital electric signal output from the A / D conversion unit 40 is 4096 gradation expressed by 12 bits.
[0018]
The A / D converter 40 is provided with a plurality of output terminals 41. The output terminal 41 is provided with twelve D0 to D11 corresponding to the output value of the digital electric signal output from the A / D converter 40 when the output is 12 bits.
The output terminal 41 of the A / D conversion unit 40 and the input terminal of the image data creation unit 35 are connected by a connection line 42 that electrically connects them. That is, the A / D conversion unit 40 and the image data creation unit 35 are connected by 12 connection lines.
[0019]
The delay circuits 50 are connected to the 12 connection lines every other line. The delay circuit 50 is a circuit composed of a resistance element 51 and a capacitor element 52. The resistance element 51 and the capacitor element 52 constituting the delay circuit 50 have the same resistance value and capacitance. By arranging the delay circuit 50 having the resistance element 51 and the capacitor element 52 in the connection line 42, the speed of the current flowing through the connection line 42 is changed, and the timing at which the digital electric signal is output from the adjacent output terminal is shifted. Occurs.
[0020]
A clock signal is supplied to the A / D converter 40 from a clock signal supply means (not shown). The A / D converter 40 outputs a digital electric signal in synchronization with the supplied clock signal. An “Hi” signal or a “Low” signal is output from the output terminal 41 of the A / D converter 40 in synchronization with the clock signal.
For example, as shown in FIG. 3, at t0, the output gradation of the digital electric signal output from the A / D converter 40 is “Hi” in synchronization with the clock signal from the two output terminals D0 and D1. ”Signal is output, and the“ Low ”signal is output from the 10 output terminals D2 to D11.
[0021]
Further, at t1, the output gradation of the digital electric signal output from the A / D converter 40 changes, and the “Hi” signal is output from the eight terminals D0 to D7, and from D8 to D11. It is assumed that a “Low” signal is output from the four terminals. At this time, the six terminals from D2 to D7 shift from the “Low” signal to the “Hi” signal in synchronization with the clock signal.
[0022]
When the delay circuit 50 is not disposed on the connection line 42 that connects the A / D conversion unit 40 and the image data creation unit 35 as in the prior art, a digital electrical signal output from an adjacent output terminal is a clock signal. At the same time, “Low” is shifted to “Hi” or “Hi” is shifted to “Low”. Therefore, EMI generated when the digital electrical signal shifts from “Low” to “Hi” or from “Hi” to “Low” is amplified.
[0023]
On the other hand, by arranging the delay circuit 50, digital electric signals output from adjacent terminals, for example, D0 and D1, or D1 and D2, etc., are slightly shifted in time as shown in FIG. Therefore, digital electric signals output from adjacent terminals do not simultaneously shift from “Low” to “Hi” or “Hi” to “Low” in synchronization with the clock signal. As a result, EMI amplification is reduced. Note that the time lag generated in the electrical signal output by the delay circuit 50 is within a few nanoseconds. For example, in the case of an RC circuit composed of a resistance element and a capacitor element, the delay time is about several nanoseconds by applying a resistance element having a resistance of several hundreds Ω and a capacitor element having a capacitance of several pico F capacitor element. Can be set.
[0024]
Next, the operation of the image reading apparatus 1 described above will be described.
The user places the document 2 desired to be read on the document table 11, and enters the image reading apparatus 1 via a driver program for controlling the image reading apparatus 1 such as TWAIN activated by the personal computer 3. On the other hand, an instruction to start reading the document 2 is given.
[0025]
When the user gives an instruction to start reading the document 2, the CPU 31 turns on the light source 22. Then, the CPU 31 controls the driving device 21 to move the carriage 20 in the sub scanning direction at a constant speed. The light reflected by the document 2 is incident on the line sensor 25, and the incident light is converted into electric charges and accumulated. The accumulated charges are transferred to a shift register (not shown) of the line sensor 25 by a drive signal generated every predetermined time, and an electric signal for one line is output from the line sensor 25. The digital image data corrected by the image data creation unit 35 is output to the personal computer 3 via the interface 14.
The document 2 is read by repeating the above processing while moving the carriage 20 in the sub-scanning direction at a constant speed.
[0026]
As described above, according to the image reading apparatus 1 according to the first embodiment of the present invention, the delay circuit 50 is disposed on the connection line 42 that connects the A / D conversion unit 40 and the image data creation unit 35. . As a result, a deviation occurs in the rising or falling timing of the digital electric signal, and the digital electric signal is not output from the A / D converter 40 at the same time. Therefore, the digital electric signal output from the A / D conversion unit 40 does not simultaneously shift from “Low” to “Hi” or “Hi” to “Low”, so that EMI amplification can be reduced. . Therefore, it is possible to prevent noise from being included in the image data created by the image data creation unit 35 and to improve the image quality of the image read by the image reading device 1.
[0027]
EMI is generated when digital electric signals output from adjacent terminals are synchronized. Therefore, in the first embodiment, EMI amplification can be reduced by arranging the delay circuits 50 every other connection line 42. Since the resistance element 51 and the capacitor element 52 disposed in the delay circuit 50 are small and inexpensive, an increase in manufacturing cost of the image reading apparatus 1 can be suppressed. Further, the delay circuit 50 can be disposed on the substrate of the image reading apparatus 1 and does not require a filter or shield for shielding EMI. Therefore, not only the manufacturing cost does not increase, but it is not necessary to secure a space for arranging the filter and the shield in the image reading device 1, and the image reading device 1 is not enlarged.
[0028]
(Second embodiment)
An image reading apparatus according to a second embodiment of the present invention will be described.
In the image reading apparatus of the second embodiment, delay circuits are arranged on all connection lines that connect the A / D conversion unit and the image data creation unit. In the second embodiment, the resistance elements and the capacitor elements constituting the delay circuit have different resistance values and capacitances. For this reason, digital electric signals flowing through the connection lines are output from the A / D converter at different timings.
In the second embodiment, the rising or falling timing of the digital electric signal can be shifted in all the connection lines, so that the EMI amplification can be more effectively reduced.
[0029]
In the above-described embodiments of the present invention, the case where a reflective original such as paper is read using a flat bed type image reading apparatus has been described. However, the present invention can be applied not only to a flat bed type image reading apparatus but also to a sheet feed type image reading apparatus, and not only to a reflective original but also to an image reading apparatus that reads a transparent original such as a film. it can.
[Brief description of the drawings]
[0030]
FIG. 1 is a schematic diagram illustrating an A / D conversion unit, an image data creation unit, and a delay circuit of an image reading apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic block diagram showing an image reading apparatus according to a first embodiment of the present invention.
FIG. 3 is a schematic diagram showing digital electrical signals output from an A / D converter of the image reading apparatus according to the first embodiment of the present invention.
FIG. 4 is a schematic diagram illustrating a conventional A / D conversion unit and an image data creation unit.

Claims (4)

An imaging unit mounted on a carriage that moves relative to a document, receives light from the document, and outputs an analog electrical signal according to the intensity of the incident light;
An A / D converter that is mounted on the carriage, has a plurality of output terminals, and converts an analog electrical signal output from the imaging means into a digital electrical signal;
An image data creation unit that is mounted on a main body on which the document is placed and that creates digital image data from a digital electrical signal output from the A / D conversion unit;
A plurality of the output terminals and the image data generation unit are mounted on the carriage and the timings of rising or falling of the plurality of digital electric signals output in synchronization from the A / D conversion unit are made uneven. A delay circuit that reduces EMI caused by an electrical signal transmitted through a connection line that electrically connects the
An image reading apparatus comprising: The delay circuit, the image reading apparatus according to claim 1, characterized in that it is arranged on one every other of the plurality of the connection lines. The image reading apparatus according to claim 1, wherein the delay circuit includes a resistance element and a capacitor element. The image reading apparatus according to claim 2, wherein the delay circuit includes a resistance element and a capacitor element, and a resistance value of the resistance element and a capacitance value of the capacitor element are the same.

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